Coated articles are known in the art for use in window applications such as insulating glass (IG) window units, vehicle windows, monolithic windows, and/or the like. In certain example instances, designers of coated articles often strive for a combination of desirable visible transmission, desirable color, low emissivity (or emittance), low sheet resistance (Rs), desirable LSG values, and/or desirable U-values in the context of IG window units. Desirable visible transmission and desired coloration may permit coated articles to be used in applications where these characteristics are desired such as in IG or vehicle window applications, whereas low emissivity and low sheet resistance permit such coated articles to block significant amounts of IR radiation so as to reduce for example undesirable heating of vehicle or building interiors.
Low-E coatings are typically deposited on a glass substrate by sputtering. Emissivity and/or sheet resistance values of a coating or coated article are driven in large part by the IR reflecting layer(s) which is/are typically made of silver or the like. However, it has been difficult to achieve low tolerance variation with respect to emissivity values of such coatings. In other words, a problem in the art has been difficulty in achieving a desired low emissivity value and/or sheet resistance value within a given small tolerance variation. The tolerance variation has been larger than desired.
In view of the above, it will be appreciated that there exists a need in the art for a coated article including a low-E coating that is designed so that a desired low emissivity value can be achieved within a given small tolerance range (e.g., a tolerance of plus/minus 1%). It would also be desirable to provide such a coating that also achieves one or more of: high visible transmission, low emissivity, thermal stability upon optional heat treatment such as thermal tempering, a low U-value, and desirable coloration and/or reflectivity values.
Conventionally, it has been difficult to achieve desirable LSG values and low ΔE* values (e.g., glass side reflective) in coatings having two silver based IR reflecting layers. In example embodiments of this invention, it has surprisingly been found that desirable LSG values and low ΔE* values (e.g., glass side reflective) in coatings having two silver based IR reflecting layers are achievable, in combination with other desirable optical characteristics, when the following are combined: (a) the second IR reflecting layer comprising silver is thicker than the first IR reflecting layer comprising silver, more preferably when second IR reflecting layer is at least 10 angstroms (Å) thicker (more preferably at least 20 angstroms thicker, even more preferably at least 30 angstroms thicker, and most preferably at least 40 angstroms thicker) than the first IR reflecting layer comprising silver; (b) provision of the bottom dielectric portion including a layer of or including silicon zirconium oxynitride, (c) center dielectric portion including a layer(s) of or including zinc stannate; (d) a zirconium silicon oxynitride based layer in the bottom dielectric portion of the layer stack is thicker (preferably at least 10 angstroms thicker, more preferably at least 20 angstroms thicker, and most preferably at least 30 angstroms thicker) than is a zinc stannate based layer in the bottom dielectric portion of the layer stack; (e) at least one zinc stannate based layer in the center dielectric portion of the layer stack is thicker (preferably at least 20 angstroms thicker, more preferably at least 40 angstroms thicker, and most preferably at least 60 angstroms thicker) than is a zirconium silicon oxynitride based layer in the bottom dielectric portion of the layer stack; and optionally (f) the absorber 14 in the center stack sandwiched between a pair of silicon nitride inclusive layers 13, 13′.
In certain example embodiments of this invention, it has been found that the combination of at least the bottom dielectric portion including a layer of or including silicon zirconium oxynitride, and center dielectric portion (between IR reflecting layers) including a layer of or including zinc stannate, allows for a combination of desirable visible transmission, consistent and low emissivity values, thermal stability upon optional heat treatment such as thermal tempering, desirable U-value, desirable LSG value, and desirable coloration and/or reflectivity values to be achieved. In certain example embodiments, an absorber layer sandwiched between a pair of dielectric layers may be provided in order to tailor visible transmission such as when lower visible transmission coatings are desired. A layer of or including zirconium silicon oxynitride in the lower dielectric portion of the coating, between the glass substrate and the lowermost IR reflecting layer (e.g., of silver or the like) improves the quality of the IR reflecting layer thereby permitting the coated article to realized low emissivity values with low tolerance variations. Providing zirconium silicon oxynitride under a layer of or including zinc stannate and under a layer of or including zinc oxide, in the lower dielectric portion of the coating, has surprisingly been found to improve the quality of the silver and thus lower emissivity values and lower emissivity tolerance values in a desirable manner. Even though the zirconium silicon oxynitride is not directly contacting the IR reflecting layer, it still improves the quality of the overlying IR reflecting layer thereby permitting thermal properties of the coating to be improved and manufactured in a more consistent manner. The IR reflecting layer has been found to grow better and have a smoother base which can more easily be repeated on a consistent basis. It has also been found that the provision of a layer of or including titanium oxide (e.g., TiO2) over the zirconium silicon oxynitride results in an increase in visible transmission of the coated article and improved optical properties if desired, as well as an increase in line speed.
In an example embodiment of this invention, there is provided a coated article including a coating supported by a glass substrate, the coating comprising moving away from the glass substrate: a dielectric layer comprising zirconium silicon oxynitride; a first layer comprising zinc stannate; a first layer comprising zinc oxide located over and directly contacting the layer comprising zinc stannate; a first infrared (IR) reflecting layer comprising silver located on the substrate over and directly contacting the first layer comprising zinc oxide; and a contact layer comprising metal oxide located over and directly contacting the first IR reflecting layer comprising silver; a second layer comprising zinc stannate on the glass substrate over at least the first IR reflecting layer and the contact layer; a second layer comprising zinc oxide located over at least the second layer comprising zinc stannate; a second IR reflecting layer comprising silver located over at least the first IR reflecting layer, the first and second layers comprising zinc stannate, and the first and second layers comprising zinc oxide; another dielectric layer over at least the second IR reflecting layer comprising silver; wherein the coating contains two silver based IR reflecting layers; wherein the second IR reflecting layer comprising silver is at least 10 angstroms (Å) thicker than the first IR reflecting layer comprising silver; wherein the dielectric layer comprising zirconium silicon oxynitride is at least 10 angstroms (Å) thicker than the first layer comprising zinc stannate; and wherein the second layer comprising zinc stannate is at least 20 angstroms (Å) thicker than the dielectric layer comprising zirconium silicon oxynitride.